The present invention relates to transmission and reception of audio and video signals and, more particularly, to a method and system for transmitting and receiving multiple audio frequency signals, preferably together with a video signal, within a frequency band allocated for a single television channel for commercial as well as subscription television, and to a multiple signal scrambling technique for secure transmission.
The transmission and reception of information in the frequency spectrum set aside for television has progressed to a point where viewers are provided with information of an audio or video nature in addition to the normal audio and video signals associated with a particular television program. Ordinarily, the normal television video signal is transmitted with an associated audio signal within an allocated frequency band of about 6 MHz. Recently, however, additional information has been transmitted and received by individual viewers with the normal audio and video signals, particularly in subscription television (STV).
Most STV systems, for example, include a video signal which is scrambled for certain subscription programs, an audio signal associated with the scrambled video signal, and an additional audio channel usually referred to as a barker channel. The barker channel is transmitted at the normal audio center frequency within the band allocated to a television channel. The barker is normally used for messages related to unscrambled video available to all viewers but unrelated to subscription television programs that are scrambled. The audio related to the scrambled subscription television programs is transmitted at a center frequency displaced from the normal audio center frequency and thus cannot be detected by the normal television receiver. Accordingly, a subscription television system may include a video signal at its normal location in the allocated frequency band (but scrambled) and two audio signals, one at the normal audio frequency position in the television channel frequency band and the other displaced from the normal television audio frequency location.
The normal television bandwidth allocated to a paticular channel also may be used to transmit additional information, related or unrelated to the television program video, where captions or other textual data is provided. For example, in captioning and teletext systems, information may be transmitted in the vertical interval of a normal television video signal or at some other convenient location in the signal. This additional information is broadcast in the normal television band allocated to a particular channel and is detected at the television receiver by a special adapter or decoder which then provides display of the captions or other textual material on the face of the television cathode ray tube (CRT).
Of course, other systems have been proposed in which additional information is transmitted, although not over the normal television frequency band allocated to a particular channel, in order to increase the amount of information available to a television viewer during the broadcast of a program. For example, television and FM stations often cooperate by simultaneously transmitting a television program over a normal allocated television channel and by transmitting its accompanying sound over an allocated FM radio channel. Thus, the viewer can watch a program on a normal television set while simultaneously listening to its accompanying sound in stereo using an FM receiver. A similar system has been proposed and has apparently been used to provide multi-lingual audio for a particular television program video. For example, in a system discussed in the July 1980 issue of TV World, at page 34, the ordinary television signal is apparently transmitted in the frequency band normally allocated to a television channel and an additional audio signal, in another language, is transmitted over an FM radio band. The viewer can select either the FM radio band or the normal television audio and thereby select, to accompany the program being viewed, either of two audios in different languages.
An objective of the present invention is also to provide information in addition to the normal television audio and video from which a television viewer can select. However, a primary objective is to provide such information within the normal frequency band allocated to a television channel. Moreover, an objective of the present invention is to provide a greater variety of information than has been heretofore available, without exceeding the allocated frequency bandwidth of a single television channel.
A further objective of the present invention is to provide information in addition to the normal television audio and video within a frequency band allocated to a single television channel in a manner that permits selection of a desired type of information by only those who are subscribers and thus eligible to receive that information.
It is therefore a more specific object of the present invention to provide a novel method and system for transmitting and receiving television signals within a normal frequency band allocated to a television channel wherein a television program video signal and at least three other signals are transmitted and can be selectively received.
Another object is to provide a novel scrambling and transmission technique for plural signals wherein the plural signals are transmitted in a minimum frequency bandwidth in a format secure from reception in an intelligible form by a normal receiver but are available on a selective basis to eligible individuals having decoders.
Yet a further object of the present invention is to provide a novel television transmission and reception method and system especially for subscription operation in which subscribers may select between a plurality of multilingual audio soundtracks accompanying the television video program material.
Still a further object of the present invention is to provide a subscription television system and method wherein highly secure transmission of the STV program material is effected by low level, relatively low security scrambling of the video portion of the television program and high level, highly secure scrambling of the audio portion of the program, and wherein one of a plurality of audio signals may be selected by eligible subscribers.
Briefly, one aspect of the present invention involves the scrambling of a plurality of input signals for secure transmission thereof of modulating in phase and quadrature components of at least one carrier signal with one and then another of the plurality of input signals in an alternating fashion such that neither that in phase nor the quadrature component contains the one or the other of the input signals in its entirety. More specifically, an in phase component of at least one carrier signal is modulated in response to one and then another of the plurality of input signals in a sequence of time intervals such that parts but not all of the one and another of the input signals are carried by the in phase component. A quadrature component of the at least one carrier signal is modulated in response to the one and another of the plurality of inputs signals in the same sequence of time intervals such that parts but not all of the one and another input signals are carried by the quadrature component and such that the in phase and quadrature components together carry the one and another of the input signals in their entireties. The modulated in phase and quadrature components are then combined for tranmission, for example, by summing the in phase and quadrature components and modulating a second carrier signal with the sum signal. The sequence of time intervals preferably comprises time intervals that vary in duration in a predetermined pseudo random manner. The input signals are preferably information signals with at least one information signal being an audio program signal associated with a television video program. In accordance with one embodiment, four input signals are scrambled by using the in phase and quadrature components of two carrier signals displaced in frequency by an amount sufficient to prevent interference in transmission. A subscriber to the scrambled transmission system may therefore choose between a number of available signals, including various language soundtracks accompanying a television video program.
In accordance with another aspect of the invention, normal audio and video program signals are transmitted in the respective normal audio and video signal frequency bands of an overall television frequency band allocated for transmission of a single television channel. The audio and video program signals are normal in the sense that they are transmitted at respective normal audio and normal video center frequencies assigned for transmission of the audio and video signals within the normal television audio and video frequency bands. Simultaneously with the transmission of the normal audio and video program signals, a plurality of additional audio signals (i.e., at least two) are transmitted in the normal audio frequency band, and within the overall television frequency band, at at least one center frequency displaced from the normal audio center frequency sufficiently so that there is no interference between the normal and additional audio signals in the transmission thereof. Moreover, the additional audio signals are transmitted in a manner that does not permit the transmitted energy to exceed the overall television frequency band.
Other aspects of the present invention include methods and systems for operating television systems with normal and additional audio signals either in scrambled or unscrambled forms for commercial television or STV services. Moreover, further features include billing and category selection (subscriber eligibility) methods and systems, as well as ways of providing eligibility and other codes, such as through addressing of individual decoders.
The foregoing and other objects and advantages of the present invention will become apparent to one skilled in the art to which the invention pertains from the following detailed description when read in conjunction with the appended drawings.